1. Field of the Invention
This invention relates in general to offshore oilfield equipment, and in particular to a tieback connector for connecting well casing located in the well to a string of casing extending down from the surface to a subsea wellhead.
2. Description of the Prior Art
This invention deals with subsea wells having a wellhead located at the sea floor. In these types of wells, the well is drilled to a first depth, then large diameter casing is installed and cemented in place. Then the well will be drilled to a second depth, and a second string of casing will be cemented in place. The diameter of the second string may be 95/8 inches. Both strings of casing will be supported at the wellhead by means of casing hangers. A riser will extend from the wellhead to the surface vessel.
In one technique, a third string of casing, which might be 7 inches in diameter, is lowered into the well, and hung off at the lower end of the second string. The 7 inch string of casing will extend completely to the surface vessel, which would likely be a tension leg platform. A tieback connector will be located in the 7 inch casing string and positioned at the wellhead. The tieback connector allows the 7 inch casing to be disconnected at the wellhead, if necessary. When disconnected, the 7 inch casing above the wellhead can be retrieved to the surface vessel. Later, a new connection can be made.
Improvements to this system are desirable. One improvement would be to provide protection means so as to avoid damaging any latching profiles for the tieback connector while drilling the well for the 7 inch casing. Another desirable feature would be to have protection means to assure that the tieback threads are not damaged when lowering the upper portion of the tieback connector on reconnection. Another desirable feature would be to provide means for releasing the upper portion of the tieback connector in case the tieback threads cannot be loosened. It would also be desirable to have a second set of tieback threads for use in the event damage happened to the primary set, or if they were removed during an emergency releasing procedure.